This invention is directed to a tool for "dimpling" the end of a tube in a controlled manner, without deforming the tube end in such a manner that it is completely out of round. In the past, boiler tubes have been connected to drums by first inserting a tube end into a hole in the lower portion of the drum. A worker located in the drum interior then would manually strike the end of the tube a number of times until the tube end becomes so deformed that the tube would hang by itself from the drum. The lower tube end would then be inserted into a hole in the upper portion of a lower drum. At this point the tube would be hanging from the top drum supported by the deformed end, along with innumerable similar such tubes. The next step generally involved expanding the tube end by a rolling operation, in which the end of the tube is flared, or expanded into tight engagement with the walls of the opening in the drum.
Certain boiler constructions today make it a requirement to weld the tube ends into the drum. In order to maintain high quality welds, it is necessary that the tube ends be round, within limits. Under the old method of deforming the tube ends, this required an additional step of rerounding the deformed tube end prior to welding.